1. Field of the Invention
The invention relates to a surgical system and, more particularly, to method and apparatus for controlling a haptic device.
2. Description of Related Art
Minimally invasive surgery (MIS) is the performance of surgery through incisions that are considerably smaller than incisions used in traditional surgical approaches. For example, in an orthopedic application such as total knee replacement surgery, an MIS incision length may be in a range of about 4 to 6 inches whereas an incision length in traditional total knee surgery is typically in a range of about 6 to 12 inches. As a result of the smaller incision length, MIS procedures are generally less invasive than traditional surgical approaches, which minimizes trauma to soft tissue, reduces post-operative pain, promotes earlier mobilization, shortens hospital stays, and speeds rehabilitation.
MIS presents several challenges for a surgeon. For example, in minimally invasive orthopedic joint replacement, the small incision size reduces the surgeon's ability to view and access the anatomy, which increases the complexity of sculpting bone and assessing proper implant position. As a result, accurate placement of implants may be difficult. Conventional techniques for counteracting these problems include, for example, surgical navigation, positioning the leg for optimal joint exposure, and employing specially designed, downsized instrumentation and complex surgical techniques. Such techniques, however, typically require a large amount of specialized instrumentation, a lengthy training process, and a high degree of skill. Moreover, operative results for a single surgeon and among various surgeons are not sufficiently predictable, repeatable, and/or accurate. As a result, implant performance and longevity varies among patients.
Conventional efforts to facilitate the performance and improve the outcome of minimally invasive and traditional orthopedic joint procedures may include the use of a robotic surgical system. For example, some conventional techniques include autonomous robotic systems, such as the ROBODOC system (formerly available from Integrated Surgical Systems, Inc., Sacramento, Calif.). Such systems, however, typically serve primarily to enhance bone machining by performing autonomous cutting with a high speed burr. Although such systems enable precise bone resections for improved implant fit and placement, they act autonomously (rather than cooperatively with the surgeon) and thus require the surgeon to cede a degree of control to the robot. Additional drawbacks of autonomous systems include the large size of the robot, poor ergonomics, increased incision length for adequate robot access, and limited acceptance by surgeons and regulatory agencies due to the autonomous nature of the system. Such systems also typically require rigid clamping of the bone during registration and cutting and thus lack real-time adaptability to the dynamic intraoperative scene.
Other conventional robotic systems include non-autonomous robots that cooperatively interact with the surgeon, such as the ACROBOT system (The Acrobot Company Limited, London, Great Britain). One drawback of conventional interactive robotic systems, however, is that such systems lack the ability to adapt surgical navigation in real-time to a dynamic intraoperative environment. For example, U.S. Pat. No. 7,035,716, which is hereby incorporated by reference herein in its entirety, discloses an interactive robotic system programmed with a three-dimensional virtual region of constraint that is registered to a patient. The robotic system includes a three degree of freedom (3 DOF) arm having a handle that incorporates force sensors. The surgeon utilizes the handle to manipulate the arm and move the cutting tool. Moving the arm via the handle is required so that the force sensors can measure the force being applied to the handle by the surgeon. The measured force is then used to control motors to assist or resist movement of the cutting tool. For example, during a knee replacement operation, the femur and tibia of the patient are fixed in position relative to the robotic system. As the surgeon applies force to the handle to move the cutting tool, the interactive robotic system applies an increasing degree of resistance to resist movement of the cutting tool as the tool approaches a boundary of the virtual region of constraint. In this manner, the robotic system guides the surgeon in preparing the bone by maintaining the tool within the virtual region of constraint. As with the above-described autonomous systems, however, the interactive robotic system functions primarily to enhance bone machining. Additionally, the 3 DOF configuration of the arm and the requirement that the surgeon manipulate the arm using the force handle results in limited flexibility and dexterity, making the robotic system unsuitable for certain MIS applications. The interactive robotic system also requires the anatomy to be rigidly restrained and the robotic system to be fixed in a gross position and thus lacks real-time adaptability to the intraoperative scene.
Although some interactive robotic systems may not require fixation of the anatomy, such as the VECTORBOT system (BrainLAB, Inc., Westchester, Ill.), such systems do not enable bone sculpting but instead merely function as intelligent tool guides. For example, such systems may control a robotic arm to constrain movement of a drill along a pre-planned drilling trajectory to enable a surgeon to drill a hole in a vertebra for placement of a pedicle screw. Similarly, other robotic systems, such as the BRIGIT system (Zimmer, Inc., Warsaw, Ind.), simply position a mechanical tool guide. For example, the robotic system disclosed in International Pub. No. WO 2005/0122916, and hereby incorporated by reference herein in its entirety, discloses a robotic arm that positions a mechanical tool guide. Using the robot-positioned tool guide, the surgeon manually manipulates a conventional surgical tool, such as a saw or drill, to make cuts to the patient's anatomy while the robot constrains movement of the tool guide. Although such systems may increase the accuracy and repeatability of the bone cuts, they are limited to performing the functions of a conventional tool guide and thus lack the ability to enable the surgeon to sculpt complex shapes in bone, as may be required for minimally invasive modular implant designs.
Some non-robotic conventional surgical tools useful for bone sculpting do not require fixation of the relevant anatomy, such as the Precision Freehand Sculptor (Blue Belt Technologies, Inc., Pittsburgh, Pa.). One drawback of such tools, however, is that they do not function in a manner that is transparent to the user. For example, U.S. Pat. No. 6,757,582, which is hereby incorporated by reference herein in its entirety, discloses a handheld surgical tool that can be used for sculpting a target shape into a bone. The handheld tool is a freehand cutting tool that is manipulated by the surgeon to grind away portions of the bone to form a desired target shape in the bone. The target shape is defined, for example, by a voxel-based model that is registered to the physical bone. During cutting, both the bone and the cutting tool are tracked to enable a controller to determine whether the cutting tool is impinging on the boundaries of the target shape and therefore cutting away bone that should be left intact. If so, the controller may shut off or retract the cutting tool to protect the bone. Although the bone is protected, the operation of the surgical tool is interrupted during the surgical procedure and the length of time to perform the procedure may increase. Further, interruption of cutting may also result in a rough surface cut. Additionally, such systems merely disable the cutting tool based on a position of the tool relative to the target shape but do not actually constrain the surgeon's manipulation of the cutting tool, for example, to prevent contact between the cutting tool and sensitive anatomy, or address other adverse situations, such as when rapid motion of the anatomy is detected. Thus, such systems may not include adequate safeguards to protect the patient. Moveover, a handheld tool that incorporates a shutoff mechanism may be bulky and heavier than a normal freehand tool or a gravity compensated interactive arm. Thus, it may be difficult for a surgeon to maneuver such a handheld tool to produce fine cutting motions, which makes such tools unsuited for applications that require complex shapes to be sculpted in bone, especially in a minimally invasive surgical environment such as when cutting in the gap between the femur and the tibia in a knee replacement operation without dislocating or distracting the joint.
In view of the foregoing, a need exists for a surgical system that is able to cooperatively interact with a surgeon to enable the surgeon to sculpt complex shapes in bone in a minimally invasive manner and that has the ability to dynamically compensate for motion of objects in the intraoperative environment in a manner that safeguards the patient and is substantially transparent to the surgeon.